This invention relates to laser heads which utilize Nd:YAG rods for converting incoherent light from laser diodes to coherent light in a side-pumped geometry. In such arrangements, one or more rows of diodes are placed or positioned along the length and parallel to the axis of the laser rod, and the rod is pumped in a direction perpendicular to that of the propagation in the laser resonator mode.
Side pumping, as it is known, has often been suggested for stimulating laser rods. However, the utilization of the diode energy in this mode has traditionally been accompanied by low efficiency, including the loss of the diode energy, for many reasons including the difficulties of exciting the rod core in the side pumping geometry. The divergence angle of the light from the diodes has increased the difficulties encountered in optimizing the light concentration at the laser rod core and has, in many instances, resulted in the application of complex optical interfaces which, themselves, contribute to losses in efficiency.
The cooling of the diode banks has also provided difficulties. Attempts to cool by heat sink alone and/or heat sink accompanied by thermoelectric cooling have, by and large, failed to consider the total wattage which must be dissipated and failed to consider the limited tolerances of such photoelectric diode banks to rising operating temperatures at the diodes. Heat sinks are effective only where there is provision for removal heat from the sink at a rate which equals the rate of heat input. Lack of temperature stability results in changes in diode operating modes, translating directly into decreased efficiency of the laser.
Attempts to pump laser rods simultaneously by a plurality of diode banks have resulted in the creation of isolated regions of excitement or hot spots within the laser rod. Such prior art banks have failed to create within the laser rod core a symmetry of excitement which approaches that achievable. Further, many such side pumping arrangements are incapable of high average power and/or continuous wave (CW) stimulation due to insufficient excitation and/or inadequate cooling arrangements for the diode banks.
Precision laser heads further suffer from a high cost of manufacture and production due to the use of a large number of dissimilar parts and the general lack of symmetry in the design of the head. Further, such designs are subject to thermal distortion of the lasing rod due to differential cooling. Some lack optimum orientation of the axis or axes of excitation with respect to the conventional "P" and "S" axes of polarization. Further, such arrangements lack the ability to be multiplexed in any arrangement in which two or more laser heads are axially stacked, with relatively rotated polarization axes.